Device for measuring the phase angle between a sine wave signal and a cyclic logic signal of the same frequency

ABSTRACT

According to the invention, on the basis of a logic signal of frequency F a multiplier processes a signal of frequency 4F sampling a A/D converter, which supplies at its outputs the digital values and a bit representing the sign of sin .0. and cos .0.. These values, processed by a circuit, are restored by two registers, which supply the absolute values of A sin .0. and A cos .0.. These values are compared in a comparator and as a function of the ratio |sin .0.|/|cos .0.| an inverting PROM and a multiplier calculate either |tan .0.| or |cot .0.|. The phase angle .0. is extracted by a PROM knowing |tan .0.| or |cot .0.| and the sine and cosine signs.

BACKGROUND OF THE INVENTION

The invention relates to a device for measuring the phase angle betweena sine wave or sinusoidal signal and a periodic or cyclic logic signalof the same frequency as the sine wave signal. It is applicable tosynchronizer systems and more specifically to systems for controllingthe synchronization of television lines in magnetoscopes.

In known devices, the phase angle, i.e. the displacement angle betweentwo waves of the same frequency, is measured in an analog manner, whichis less accurate than the device according to the invention which isbased on a digital process. For example, the device according to theinvention achieves an accuracy in the measurement of the phase anglesuch that a clock of above 1 GHz would be necessary in the case of aknown device to obtain the same accuracy. Such measuring systems are notat present widely used. Through digitizing the measurements on the sinewave signal, it is possible to relatively easily obtain a very highdegree of precision in the device according to the invention.

Fundamentally, the device according to the invention converts the sinewave signal at frequency F into a digital signal by means of ananalog-digital converter sampled by the logic signal with which thephase angle is to be measured, said logic signal having a samplingfrequency equal to 4 times that of the sine wave signal F. Two samplesare measured on each sinusoidal half-cycle, the first sample giving avalue representing the sine of the phase angle .0. and the second samplegiving a value representing the cosine of the phase angle .0., displacedby π/2 and on the basis of which angle .0. can easily be calculated.

One of the original features of the device according to the invention isthat the measurement of the angle .0. is independent of the amplitude ofthe sine wave signal, because the device either measures the tangent orthe cotangent of angle .0. in absolute values, thus eliminating theamplitude A of the sine wave signal. Thus, the calculation of thetangent or cotangent of the angle .0., whilst forming the ratio of thesine to the cosine or vice versa, means that it is only necessary totake account of those parts in which the tangent or cotangent are linearfunctions. For this reason, the device according to the inventionmeasures the absolute values of the sine and cosine of the angle and, asa function of the ratio obtained, it calculates either the tangent orthe cotangent in such a way that it only works in the linear parts ofthese functions. Another original aspect of the device is that theprecision obtained is only dependent on the number of bits of theanalog-digital converter.

BRIEF SUMMARY OF THE INVENTION

More specifically, the present invention relates to a device formeasuring the phase angle between a sine wave signal and a cyclic logicsignal of the same frequency with, on the input of the sine wave signal,an analog-digital sampling converter, wherein it comprises:

a frequency multiplying circuit, which transforms the cyclic logicsignal of frequency F into a cyclic logic signal of frequency 4F for thepurpose of sampling the A-D converter at a rate of 2 samples perhalf-cycle of the sine wave signal, said samples being representative ofsin .0. and cos .0., displaced by π/2;

a circuit for extracting from the sample supplied by the A-D converterabsolute values of A sin .0. and A cos .0., A being the amplitude of thesine wave signal, as well as the signs of sin .0. and cos .0.;

a circuit for calculating the absolute value of tan .0. or cot .0. onthe basis of the absolute value of A sin .0. and A cos .0., as afunction of whether A sin .0.<A cos .0. or A sin .0.>A cos .0., with theelimination of the amplitude A;

an accumulator which stores a plurality of data tan .0. or cot .0. andrestores a mean value therefrom;

a programmable read only memory receiving on its inputs digital datarepresenting tan .0. or cot .0., from the operation performed either intan .0. or cot .0., of the sign of cos .0. and the sign of sin .0., andwhich supplies at its outputs digital information representing the phaseangle .0..

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in greater detail hereinafter relativeto non-limitative embodiments and the attached drawings, wherein show:

FIG. 1 a block diagram of the phase angle measuring device according tothe invention.

FIG. 2 curves representing the sine wave signal and the logic samplingsignal.

FIGS. 3 and 4 the useful working areas on the curves of tangents .0. andcotangents .0..

FIG. 5 a diagram illustrating the extraction by an analog-digitalconverter of the sine .0. and cosine .0. data.

FIG. 6 a block diagram of the device according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a highly simplified block diagram of the phase angle measuringdevice according to the invention. A sine wave signal of frequency Fapplied to the input terminal 1 of an amplifier 2 is transmitted to ananalog-digital converter 3 with n conversion bits. In parallel, a squarewave logic signal of the same frequency F as the sine wave signal isapplied to the input terminal 4 of a frequency multiplier by four 5,which thus supplies a logic signal of frequency 4F used for sampling theanalog-digital converter 3. The output signal of the n bitanalog-digital converter is applied to a phase measuring device 6controlled by the same signal of frequency 4F as that sampled byconverter 3.

Measuring device 6 supplies information relative to the phase angle .0.,which will be defined hereinafter. Fundamentally, the measurement of thephase angle .0. involves the measurement of the sine and cosine of angle.0., as is shown in FIG. 2.

FIG. 2 shows the sine wave signal on curve A and the reference signal ofthe same frequency F on curve C. Curve B represents the sampling signalobtained at the output of multiplier 5 in FIG. 1 at frequency 4F. Thus,four square wave sampling signals correspond to one cycle of the sinewave signal, or two signals per half-cycle, said two signals used foreach half-wave being designated 1 and 2.

The phase displacement between the sine wave signal and the logic signalis represented on curve A by distance .0., which represents thedisplacement between the sine wave 0 and the logic zero of curve C. Thesine of the phase displacement angle .0. is measured by the number ofbits obtained at the output of the analog-digital converter sampled bythe pulse of index 1. The cosine of this angle is measured, under sameconditions, by the sample of index 2, displaced by π/2. The measurementof the sine and cosine of the phase angle .0. enables the calculation ofthe phase displacement in the range of ±π.

As the sine wave signal is of form:

    v(t)=A sin (2πFt+.0.)

the value obtained corresponding to the sample of index 1 represents Asin .0. and the value obtained corresponding to the sample of index 2represents A cos .0..

To obtain independence of the amplitude A of the sine wave signal, it ismerely necessary to form the ratio A sin .0./A cos .0., which give tan.0., or the ratio A cos .0./A sin .0., which gives cot .0..

Thus, as shown in FIGS. 3 and 4, only part of the curves representingtan .0. and cot .0. can be used for accurately measuring the angle .0..

FIG. 3 shows the curve of tan .0. as a function of the angle and it ispointed out that only that part of the curve corresponding to a rangebetween -π/4 and +π/4 can be likened to a straight line. In FIG. 4,which shows cot .0. as a function of the angle .0., it is pointed outthat in the same way only the range between π/4 and 3π/4 can be likenedto a straight line. These areas corresponding to ranges of π/2 on themeasuring range of the device which is + or -π, so that the device willcalculate, as a function of the phase angle, either a tangent or acotangent. Thus, for a phase angle between π and -(3π/4), -(π/4) and(3π/4) and +π the device calculates tg .0. and for a phase angle between-(3π/4) and -(π/4) and +(π/4) and (3π /4), the device calculates cotg.0..

The decision to calculate either the tangent or the cotangent is made bya comparator, which compares the absolute values of A sin .0. and A cos.0., so that if the absolute value |A sin .0.|<|A cos .0.|, the devicecalculates the tangent of angle .0.. while if the absolute value of |Asin .0.|>|A cos .0.|, the device calculates the cotangent of angle .0..

The values of tan .0. or cot .0. are calculated in absolute values, onthe basis of the absolute values of A sin .0. and A cos .0., on a rangeΔ.0. of ±π/4, which subdivides the measuring system into 8 zones.

    ______________________________________                                                                   3π/    5π/                                                                             3π/                                                                             7π/                         Angles  0      π/4 π/2                                                                             4    π 4    2    4   2 π                     ______________________________________                                        Zones    1      2      3    4    5    6    7    8                             Sine signs                                                                             +      +      +    +    -    -    -    -                             Cosine signs                                                                           +      +      -    -    -    -    +    +                             Calculation                                                                   of tg    Yes                Yes  Yes            Yes                           Calculation                                                                   of cotg         Yes    Yes            Yes  Yes                                ______________________________________                                    

It is possible to unambiguously determine the angle .0. in a range of ±πthrough the knowledge of the absolute values of tan .0. or cot .0., as afunction of the zone corresponding to the phase displacement angle .0.,as well as that of the signs of sin .0. and cos .0..

The following drawings provide a better understanding of the way inwhich the signs and the absolute values of the sine and cosine, tangentand cotangent are measured.

FIG. 5 shows a diagram illustrating the extraction by an analog-digitalconverter of data representing sin .0. and cos .0.. Above the curverepresenting slightly more than one cycle of the sine wave signal hasbeen plotted the logic sampling signal with a certain phase displacementcompared with the sine wave signal. The latter is broken down into two2^(n) digital values or levels between 0 and 2^(n), the analog 0 beingat level 2^(n-1) and the amplitude of the signal being within the 2^(n)digital levels.

Thus, the negative half of the wave is measured by 2^(n-1) digitallevels and the positive half of the wave is measured by 2^(n-1) digitallevels. By using a 9 bit converter, i.e. 2⁹ =512 levels, the 0 of thesine curve is located at value 256, while the negative peak is at level0 and the positive peak is at level 511. The 9 bits of the converter areused in two groups, the most significant bit 2⁸ representing the sign ofthe sample and the other bits from 2⁰ to 2⁷ represents the digital valueof the sample. Thus, the sine wave signal is broken down by a 9 bitanalog-digital converter into the digital values given in the followingtable in absolute terms.

    ______________________________________                                                          Converter outputs (bits re-                                 Digital  sign bit presenting the analog value)                                values   2.sup.8  2.sup.7                                                                             2.sup.6                                                                            2.sup.5                                                                           2.sup.4                                                                            2.sup.3                                                                           2.sup.2                                                                            2.sup.1                                                                           2.sup.0                    ______________________________________                                        511      1        1     1    1   1    1   1    1   1                          510      1        1     1    1   1    1   1    1   0                          . . .    . . .    . . .                                                       258      1        0     0    0   0    0   0    1   0                          257      1        0     0    0   0    0   0    0   1                          256 (analog                                                                            1        0     0    0   0    0   0    0   0                             zero)                                                                      255      0        1     1    1   1    1   1    1   1                          254      0        1     1    1   1    1   1    1   0                          . . .    . . .    . . .                                                       1        0        0     0    0   0    0   0    0   1                          0        0        0     0    0   0    0   0    0   0                          ______________________________________                                    

Two cases occurs.

For measurements of samples having digital values equal to or above 256,i.e. for measurements of the positive half-cycles of the sine wavesignal for which the sign bit is equal to 1, the bits 2⁰ to 2⁷ directlyrepresent the analog value. Thus, on the above table, the lines abovethose of the analog zero for which the sign bit is equal to 1 directlyrepresent the analog value of a positive half-cycle of the sine wavesignal.

For measurements on samples of digital values below 256, whichcorrespond to negative half-cycles of the sine wave signal and for whichthe sign bit is equal to zero, the bits 2⁰ to 2⁷ no longer directlyrepresent the analog value. Thus, the latter are twos complement. Inthis second case, for obtaining digital values between 0 and 256, i.e. 0to 256 equals one sign bit 2⁸ =0, it is necessary to perform the twoscomplement operation, which leads to the following digitalrepresentation.

    ______________________________________                                                          Converter outputs (bits re-                                 Digital  sign bit presenting the analog value)                                values   2.sup.8  2.sup.7                                                                             2.sup.6                                                                            2.sup.5                                                                           2.sup.4                                                                            2.sup.3                                                                           2.sup.2                                                                            2.sup.1                                                                           2.sup.0                    ______________________________________                                        511      1        1     1    1   1    1   1    1   1                          510      1        1     1    1   1    1   1    1   0                          . . .    . . .    . . .                                                       258      1        0     0    0   0    0   0    1   0                          257      1        0     0    0   0    0   0    0   1                          256 (analog                                                                            1        0     0    0   0    0   0    0   0                             zero)                                                                      255      0        0     0    0   0    0   0    0   1                          254      0        0     0    0   0    0   0    1   0                          . . .    . . .    . . .                                                       1        0        1     1    1   1    1   1    1   1                          0        0        1     1    1   1    1   1    1   1                          ______________________________________                                    

Thus, the twos complement operation of bits 2⁰ to 2⁷ is controlled bythe sign bit 2⁸.

FIG. 6 shows the diagram of the device according to the invention. Thesine wave signal of frequency F is applied, in the manner describedhereinbefore, to the input terminal 1 of an analog-digital converter 3.The latter is controlled by a digital signal of frequency 4F andaddressed at its clock gate C_(p). The output levels of the converter,i.e. sign bit 2⁸ of the bits of values 2⁰ to 2⁷ are applied to aregister 7, which is controlled by a circuit 8 which, on the basis ofthe logic signal of frequency 4F, extracts the clock signalscorresponding to the samples of indices 1 and 2 in FIG. 2.

At the output terminals of register 7, sine bit 2⁸ is directly appliedto the corresponding inputs of two other registers 9 and 10. The bits ofdigital values 2⁰ to 2⁷, i.e. n digital values are also applied to atwos complement circuit, shown within the dotted line 11 in FIG. 6. Thiscircuit receives the digital value n from register 7 at an invertingamplifier. The output value n from inverter 12 is addressed to a firstgate of an adder 13, which also receives at a second gate a digitalvalue "1". The output value n+1, which is the twos complement necessaryfor calculating the phase angles corresponding to the negative cycles ofthe sine wave signal, is addressed to a first terminal 1 of a switch 14.At a second terminal 2, the switch 14 receives the signal n directlysampled at the output of register 7. Finally, by means of a terminal 15,switch 14 is controlled by sign bit 2⁸, whose significance is 0 or 1, asa function of the phase displacement angle. The signal transmitted tothe output of the switch as a function of the sign bit value isindicated below:

    ______________________________________                                        sign bit 2.sup.8                                                                              0           1                                                 switch position switching   switching                                                         step 1      step 2                                            value transferred                                                                             -n + 1      n                                                 by switch                                                                     ______________________________________                                    

The signal transmitted by switch 14 is addressed in parallel to the twoaforementioned registers 9 and 10 controlled at their clock gates by thesine and cosine sampling signals respectively, register 9 being used forsine recording and register 10 for cosine recording.

At the output terminals of register 9 are available on the one hand sinesign information, directly from the information of sign bit 2⁸, and onthe other hand 8 bits giving the absolute value of A sin .0.. In thesame way, at the output terminals of register 10, there are on the onehand the cosine sign and on the other the absolute value of A cos .0. on8 bits.

These absolute values and the sine and cosine signs make it possible toprocess data of absolute values tan .0. or cot .0.. The decisioncriterion for the device to use either the tangent or the cotangentresults from the comparison between the absolute sine and cosine values,as indicated hereinbefore. If |A sin .0.| is below |A cos .0.|, thedevice calculates the tangent. In the opposite case, the devicecalculates the cotangent. Switching takes place automatically on thebasis of the result of a digital comparator.

The circuit for processing the absolute values of tan .0. or cot .0.comprises a comparator 16 receiving on its two input terminals 17 and 18the data from registers 9 and 10, i.e. it receives an its input terminal17 a |A sin .0.| and at its terminal 18 |A sin .0.|. Simultaneously, theinput data from comparator 16 and transmitted to two switches 21, 22.The information |A sin .0.| present on input terminal 17 of comparator16 is transmitted to a first terminal 3 of a first switch 21 and to asecond terminal 6 of a second switch 22, whilst information |A cos .0.|present on the input terminal 18 of the comparator is transmitted to asecond terminal 4 of the first switch 21 and to a first terminal 5 of asecond switch 22. Switches 21 and 22 are represented by the symbolicdiagram of an electromechanical switch. In fact, they form part ofregister 20, which is a flip-flop register with 8 bit, 3 state outputsand which in fact function like a series of switches.

The output signal of comparator 16, sampled at terminal 19 correspondsto the comparison between the absolute values of the sine and the cosineand consequently to the operation decision of the device by calculatingthen either the tangent or the cotangent of the phase angle. This outputsignal on terminal 19 is consequently addressed to register 20 and itcontrols switches 21 and 22. If the switches are in the positioncorresponding to their first terminal 3 or 5, the device calculates cot.0.. However, if the switches are as shown in FIG. 6 in the positioncorresponding to their second terminal 4 and 6, the device calculatesthe tan of the phase angle.

Thus, the decision to either calculate tan .0., or cot .0. results fromthe comparison of the absolute values of A sin .0. and A cos .0., thesignal representing this comparison and coming from terminal 19 ofcomparator 16 orienting either A sin .0. on output terminal 23 of switch21 and simultaneously A cos .0. on output terminal 24 of switch 22, orconversely A cos .0. on output terminal 23 of switch 21 and A sin .0. onoutput terminal 24 of switch 22.

This branching of the values of A sin .0. and A cos .0. is madenecessary by the fact that tan .0. and cot .0. are not calculated byforming the ratio A sin .0./A cos .0. or vice versa, but instead use adigital multiplier, i.e.: ##EQU1##

The reciprocal of the functions A sin .0. or A cos .0. is obtained bymeans of a programmable read-only memory PROM 25 positioned on theelectrical path of one of the two outputs, such as e.g. switch 21 inFIG. 6. This memory is programmed in such a way that it restores thereciprocal of the value addressed to it.

The signals from a first switch 21, followed by the inverting PROM 25and a second switch 22 are both addressed to a multiplier 26, whichtherefore carries out the multiplication in accordance with one of thetwo equations given hereinbefore. If switches 21 and 23 are at thepositions corresponding to their terminals 3 and 4, multiplier 26performs the multiplication (1/|A sin .0.|) (|A cos .0.|). If switches21 and 22 are on the positions corresponding to their terminals 4 and 6,multiplier 26 performs the multiplication (1/|A cos .0.|) (|A sin .0.|).

The output signal of multiplier 26, which is therefore the digital valueof tan .0. or cot .0., is addressed to an accumulator 27, which formsthe mean value of several values of tan .0. and cot .0., in order toimprove the signal-to-noise ratio of the output value.

The different values of tan .0. or cot .0., sine and cosine signs andcalculation decision data either by tan or by cot processed hitherto inthe circuit according to the invention makes it possible to calculatethe angle .0..

The calculation is performed by a programmable read-only memory PROM 28,which receives at its inputs 29 the information on 8 bits of tan .0. orcot .0. from accumulator 27, while receiving at its input 30 theinformation on one calculation decision bit either in tan or in cot andwhich comes from the output terminal 19 of comparator 16. Finally, itreceives at its two inputs 31, 32 on one bit the sine .0. and cosine .0.sign data. Thus, it is possible to unambiguously calculate the angle.0., whose digital value is restored on 9 bits on output terminal 33 ofPROM 28.

The device for firstly measuring the phase angle between two signals,namely a sine wave signal and a cyclic logic signal of the samefrequency as the sine wave signal, can in particular be used in thesynchronization of the scanning of the lines in a magnetoscope. Thisdevice makes it possible to correct errors in the run linked with tapespeed errors, to the extension or compression of the tape as a result oftemperature, moisture or for any other reason. However, this device canbe used more generally for the synchronization of the system in which asine wave signal has to be defined in time with respect to logic squarewave pulses or the like.

What is claimed is:
 1. A device for measuring the phase angle between asine wave signal and a cyclic logic signal of the same frequency with,on the input of the sine wave signal, an analog-digital samplingconverter, wherein it comprises:a frequency multiplying circuit, whichtransforms the cyclic logic signal of frequency F into a cyclic logicsignal of frequency 4F for the purpose of sampling the A-D converter ata rate of 2 samples per half-cycle of the sine wave signal, said samplesbeing representative of sin .0. and cos .0., displaced by π/2; a circuitfor extracting from the sample supplied by the A-D converter absolutevalues of A sin .0. and A cos .0., A being the amplitude of the sinewave signal, as well as the signs of sin .0. and cos .0.; a circuit forcalculating the absolute value of tan .0. or cot .0. on the basis of theabsolute value of A sin .0. and A cos .0., as a function of whether Asin .0.<A cos .0. or A sin .0.>A cos .0., with the elimination of theamplitude A; an accumulator which stores a plurality of data tan .0. cot.0. and restores a mean value therefrom; a programmable read only memoryreceiving on its inputs digital data representing tan .0. or cot .0.,from the operation performed either in tan .0. or cot .0., of the signof cos .0. and the sign of sin .0., and which supplies at its outputsdigital information representing the phase angle .0..
 2. A phase anglemeasuring device according to claim 1, wherein the A-D converter has two2^(n) bits, the bits between 2⁰ and 2^(n-1) supplying a digital valuerepresenting sin .0. and cos .0. and the most significant bit 2^(n)supplying the sign of the sine and the cosine in the form of a logic 0or a logic
 1. 3. A device for measuring the phase angle between the sinewave signal and a cyclic logic signal of the same frequency with, on theinput of the sine wave signal, an analog-digital sampling converter,wherein it comprises:a frequency multiplying circuit, which transformsthe cyclic logic signal of frequency F into a cyclic logic signal offrequency 4F for the purpose of sampling the A-D converter at a rate of2 samples per half-cycle of the sine wave signal, said samples beingrepresentative of sin .0. and cos .0., displaced by π/2; a circuit forextracting from the sample supplied by the A-D converter absolute valuesof A sin .0. and A cos .0., A being the amplitude of the sine wavesignal, as well as the signs of sin .0. and cos .0.; a circuit forcalculating the absolute value of tan .0. or cot .0. on the basis of theabsolute value of A sin .0. and A cos .0., as a function of whether Asin .0.<A cos .0. or A sin .0.>cos .0., with the elimination of theamplitude A; an accumulator which stores a plurality of data tan .0. orcot .0. and restores a mean value therefrom; a programmable read onlymemory receiving on its inputs digital data representing tan .0. or cot.0., from the operation performed either in tan .0. or cot .0., of thesign of cos .0. and the sign of sin .0., and which supplies at itsoutputs digital information representing the phase angle .0.; said A-Dconverter having two 2^(n) bits, the bits between 2⁰ and 2^(n-1)supplying a digital value representing sin .0. and cos .0. and the mostsignificant bit 2^(n) supplying the sign of the sine and the cosine inthe form of a logic 0 or a logic 1; said circuit for extracting absolutevalues of A cos .0. and A sin .0. comprising: a first register receivingat its input the digital values from the converter, as well as samplingdata from a circuit for sampling signals corresponding to themeasurement of sin .0. and cos .0. in the logic signal at frequency 4F,the register supplying at its output on the one hand the mostsignificant digital value representing the sign of sin .0. and cos .0.and on the other digital measuring values; a twos complements circuitfor the digital values for which the sign a is negative, said circuitcomprising an inverter followed by a ones complement adder and a switchcontrolled by the sign information from the register, the switchsupplying at its output terminal the digital values from the registerwhen the sine information is logic 1 and twos complement values when thesine information is a logic 0; a second register receiving at its inputsthe sign information from the first register, as well as the digitalvalues from the switch and which supplies at its terminals the absolutevalue of |A sin .0.| in digital form as well as the sign; and a thirdregister receiving at its inputs the sign informatioin from the firstregister, as well as digital values from the switch and supplying at itsoutputs the absolute value of |A cos .0.|, in digital form, as well asthe sign.
 4. A device for measuring the phase angle between a sine wavesignal and a cylic logic signal of the same frequency with, on the inputof the sine wave signal, an analog-digital sampling converter, whereinit comprises:a frequency multiplying circuit, which transforms thecyclic logic signal of frequency F into a cyclic logic signal offrequency 4F for the purpose of sampling the A-D converter at a rate of2 samples per half-cycle of the sine wave signal, said samples beingrepresentative of sin .0. and cos .0., displaced by π/2; a circuit forextracting from the sample supplied by the A-D converter absolute valuesof A sin .0. and A cos .0., A being the amplitude of the sine wavesignal, as well as the signs of sin .0. and cos .0.; a circuit forcalculating the absolute value of tan .0. or cot .0. on the basis of theabsolute value of A sin .0. and A cos .0., as a function of whether Asin .0.<A cos .0. or A sin .0.>A cos .0., with the elimination of theamplitude A; an accumulator which stores a plurality of data tan .0. orcot .0. and restores a mean value therefrom; a programmable read onlymemory receiving on its inputs digital data representing tan .0. or cot.0., from the operation performed either in tan .0. or cot .0., of thesign of cos .0. and the sign of sin .0., and which supplies at itsoutputs digital information representing the phase angle .0.; said A-Dconverter having two 2^(n) bits, the bits between 2⁰ and 2^(n-1)supplies a digital vaue representing sin .0. and cos .0. and the mostsignificant but 2^(n) supplying the sign of the sine and the cosine inthe form of a logic 0 or a logic 1; said circuit for calculating theabsolute values of tan .0.| and |cot .0.| comprising: a comparatorreceiving at its inputs the digital values representing |A sin .0.| and|A cos .0.|, compares them and supplies at its output |tan .0.| or |cot.0.| calculation data; a register having a plurality of flip-flops, eachof said flip-flops receiving at a first input terminal the digital valueof |A sin .0.| and at the second input terminal the digital value of |Acos .0.| and supplying at its output terminal either |A sin .0.| or |Acos .0.|, as a function of the comparison data from the output of thecomparator; a programmable read only memory receiving at its input thedata from the first output of the register and supplying at its outputthe reciprocal of said data; a multiplying circuit receiving at a firstinput the values from the programmable read only memory (1/|A sin .0.|or 1/|A cos .0.|) and at a second input the values from a second outputof the register (|A cos .0.| or |A sin .0.|) and carries out themultiplication thereof in order to supply at its output either |tan .0.|or |cot .0.|; and an accumulator receiving the values from themultiplier and supplying at its output a mean value of |tan .0.| or |cot.0.|.